In the course of the development of fluorinated elastomers, very precise requirements have been emphasized recently, namely the simultaneous attainment of the following goals:
1. An overall improvement in the rheological properties and the processability of the mixtures.
2. A decrease in the hardness of the mixtures (as compared with the Shore A value of 75 reported in Kirk Othmer--Third Edition (1980), Volume 8, page 509, as typical value for a fluoroelastomer).
3. The possibility of easily extruding products of complicated profile and also of substantial dimensions.
4. The obtaining of vulcanized products having improved properties of resistance to deformation under compression (improvement of the compression set).
5. An easily controllable cure rate.
Different types of plasticizing agents are already used in the art in order to obtain goals 1 to 3, they, however, generally giving rise to various drawbacks such as a worsening of the elastic properties, poorer heat resistance, and high values of the compression set. Better results have been obtained with the fluoroelastomer compositions in accordance with the applicant's European Pat. No. 23957; in that case, however, optimum characteristics limited to items 1-3 are obtained.